Initial refactor of framework.

mlp/costs.py

@@ -1,64 +1,105 @@
-# Machine Learning Practical (INFR11119),
+"""Model costs."""
-# Pawel Swietojanski, University of Edinburgh
 
 
-import numpy
+import numpy as np
 
 
-class Cost(object):
+class MeanSquaredErrorCost(object):
     """
-    Defines an interface for the cost object
     """
-    def cost(self, y, t, **kwargs):
-        """
-        Implements a cost for monitoring purposes
-        :param y: matrix -- an output of the model
-        :param t: matrix -- an expected output the model should produce
-        :param kwargs: -- some optional parameters required by the cost
-        :return: the scalar value representing the cost given y and t
-        """
-        raise NotImplementedError()
 
-    def grad(self, y, t, **kwargs):
+    def __call__(self, outputs, targets):
-        """
+        return 0.5 * np.mean(np.sum((outputs - targets)**2, axis=1))
-        Implements a gradient of the cost w.r.t y
-        :param y: matrix -- an output of the model
-        :param t: matrix -- an expected output the model should produce
-        :param kwargs: -- some optional parameters required by the cost
-        :return: matrix - the gradient of the cost w.r.t y
-        """
-        raise NotImplementedError()
 
-    def get_name(self):
+    def grad(self, outputs, targets):
-        return 'cost'
+        return outputs - targets
+
+    def __repr__(self):
+        return 'MeanSquaredErrorCost'
 
 
-class MSECost(Cost):
+class BinaryCrossEntropyCost(object):
-    def cost(self, y, t, **kwargs):
-        se = 0.5*numpy.sum((y - t)**2, axis=1)
-        return numpy.mean(se)
-
-    def grad(self, y, t, **kwargs):
-        return y - t
-
-    def get_name(self):
-        return 'mse'
-
-
-class CECost(Cost):
     """
-    Cross Entropy (Negative log-likelihood) cost for multiple classes
     """
-    def cost(self, y, t, **kwargs):
-        #assumes t is 1-of-K coded and y is a softmax
-        #transformed estimate at the output layer
-        nll = t * numpy.log(y)
-        return -numpy.mean(numpy.sum(nll, axis=1))
 
-    def grad(self, y, t, **kwargs):
+    def __call__(self, outputs, targets):
-        #assumes t is 1-of-K coded and y is a softmax
+        return -np.mean(
-        #transformed estimate at the output layer
+            targets * np.log(outputs) + (1. - targets) * np.log(1. - ouputs))
-        return y - t
 
-    def get_name(self):
+    def grad(self, outputs, targets):
-        return 'ce'
+        return (1. - targets) / (1. - outputs) - (targets / outputs)
+
+    def __repr__(self):
+        return 'BinaryCrossEntropyCost'
+
+
+class BinaryCrossEntropySigmoidCost(object):
+    """
+    """
+
+    def __call__(self, outputs, targets):
+        probs = 1. / (1. + np.exp(-outputs))
+        return -np.mean(
+            targets * np.log(probs) + (1. - targets) * np.log(1. - probs))
+
+    def grad(self, outputs, targets):
+        probs = 1. / (1. + np.exp(-outputs))
+        return probs - targets
+
+    def __repr__(self):
+        return 'BinaryCrossEntropySigmoidCost'
+
+
+class BinaryAccuracySigmoidCost(object):
+    """
+    """
+
+    def __call__(self, outputs, targets):
+        return ((outputs > 0) == targets).mean()
+
+    def ___repr__(self):
+        return 'BinaryAccuracySigmoidCost'
+
+
+class CrossEntropyCost(object):
+    """
+    """
+
+    def __call__(self, outputs, targets):
+        return -np.mean(np.sum(targets * np.log(outputs), axis=1))
+
+    def grad(self, outputs, targets):
+        return -targets / outputs
+
+    def __repr__(self):
+        return 'CrossEntropyCost'
+
+
+class CrossEntropySoftmaxCost(object):
+    """
+    """
+
+    def __call__(self, outputs, targets):
+        probs = np.exp(outputs)
+        probs /= probs.sum(-1)[:, None]
+        return -np.mean(np.sum(targets * np.log(probs), axis=1))
+
+    def grad(self, outputs, targets):
+        probs = np.exp(outputs)
+        probs /= probs.sum(-1)[:, None]
+        return probs - targets
+
+    def __repr__(self):
+        return 'CrossEntropySoftmaxCost'
+
+
+class MulticlassAccuracySoftmaxCost(object):
+    """
+    """
+
+    def __call__(self, outputs, targets):
+        probs = np.exp(outputs)
+        return np.mean(np.argmax(probs, -1) == np.argmax(targets, -1))
+
+    def __repr__(self):
+        return 'MulticlassAccuracySoftmaxCost'

mlp/initialisers.py

@@ -0,0 +1,66 @@
+# -*- coding: utf-8 -*-
+"""Parameter initialisers.
+
+This module defines classes to initialise the parameters in a layer.
+"""
+
+import numpy as np
+
+DEFAULT_SEED = 123456  # Default random number generator seed if none provided.
+
+
+class ConstantInit(object):
+    """Constant parameter initialiser."""
+
+    def __init__(self, value):
+        """Construct a constant parameter initialiser.
+
+        Args:
+            value: Value to initialise parameter to.
+        """
+        self.value = value
+
+    def __call__(self, shape):
+        return np.ones(shape=shape) * self.value
+
+
+class UniformInit(object):
+    """Random uniform parameter initialiser."""
+
+    def __init__(self, low, high, rng=None):
+        """Construct a random uniform parameter initialiser.
+
+        Args:
+            low: Lower bound of interval to sample from.
+            high: Upper bound of interval to sample from.
+            rng (RandomState): Seeded random number generator.
+        """
+        self.low = low
+        self.high = high
+        if rng is None:
+            rng = np.random.RandomState(DEFAULT_SEED)
+        self.rng = rng
+
+    def __call__(self, shape):
+        return self.rng.uniform(low=self.low, high=self.high, size=shape)
+
+
+class NormalInit(object):
+    """Random normal parameter initialiser."""
+
+    def __init__(self, mean, std, rng=None):
+        """Construct a random uniform parameter initialiser.
+
+        Args:
+            mean: Mean of distribution to sample from.
+            std: Standard deviation of distribution to sample from.
+            rng (RandomState): Seeded random number generator.
+        """
+        self.mean = mean
+        self.std = std
+        if rng is None:
+            rng = np.random.RandomState(DEFAULT_SEED)
+        self.rng = rng
+
+    def __call__(self, shape):
+        return self.rng.normal(loc=self.mean, scale=self.std, size=shape)

mlp/layers.py

@@ -1,561 +1,325 @@
+# -*- coding: utf-8 -*-
+"""Layer definitions.
 
-# Machine Learning Practical (INFR11119),
+This module defines classes which encapsulate a single layer.
-# Pawel Swietojanski, University of Edinburgh
 
-import numpy
+These layers map input activations to output activation with the `fprop`
-import logging
+method and map gradients with repsect to outputs to gradients with respect to
-from mlp.costs import Cost
+their inputs with the `bprop` method.
 
+Some layers will have learnable parameters and so will additionally define
+methods for getting and setting parameter and calculating gradients with
+respect to the layer parameters.
+"""
 
-logger = logging.getLogger(__name__)
+import numpy as np
-
+import mlp.initialisers as init
-
-def max_and_argmax(x, axes=None, keepdims_max=False, keepdims_argmax=False):
-    """
-    Return both max and argmax for the given multi-dimensional array, possibly
-    preserve the original shapes
-    :param x: input tensor
-    :param axes: tuple of ints denoting axes across which
-                 one should perform reduction
-    :param keepdims_max: boolean, if true, shape of x is preserved in result
-    :param keepdims_argmax:, boolean, if true, shape of x is preserved in result
-    :return: max (number) and argmax (indices) of max element along certain axes
-             in multi-dimensional tensor
-    """
-    if axes is None:
-        rval_argmax = numpy.argmax(x)
-        if keepdims_argmax:
-            rval_argmax = numpy.unravel_index(rval_argmax, x.shape)
-    else:
-        if isinstance(axes, int):
-            axes = (axes,)
-        axes = tuple(axes)
-        keep_axes = numpy.array([i for i in range(x.ndim) if i not in axes])
-        transposed_x = numpy.transpose(x, numpy.concatenate((keep_axes, axes)))
-        reshaped_x = transposed_x.reshape(transposed_x.shape[:len(keep_axes)] + (-1,))
-        rval_argmax = numpy.asarray(numpy.argmax(reshaped_x, axis=-1), dtype=numpy.int64)
-
-        # rval_max_arg keeps the arg index referencing to the axis along which reduction was performed (axis=-1)
-        # when keepdims_argmax is True we need to map it back to the original shape of tensor x
-        # print 'rval maxaarg', rval_argmax.ndim, rval_argmax.shape, rval_argmax
-        if keepdims_argmax:
-            dim = tuple([x.shape[a] for a in axes])
-            rval_argmax = numpy.array([idx + numpy.unravel_index(val, dim)
-                                       for idx, val in numpy.ndenumerate(rval_argmax)])
-            # convert to numpy indexing convention (row indices first, then columns)
-            rval_argmax = zip(*rval_argmax)
-
-    if keepdims_max is False and keepdims_argmax is True:
-        # this could potentially save O(N) steps by not traversing array once more
-        # to get max value, haven't benchmark it though
-        rval_max = x[rval_argmax]
-    else:
-        rval_max = numpy.asarray(numpy.amax(x, axis=axes, keepdims=keepdims_max))
-
-    return rval_max, rval_argmax
-
-
-class MLP(object):
-    """
-    This is a container for an arbitrary sequence of other transforms
-    On top of this, the class also keeps the state of the model, i.e.
-    the result of forward (activations) and backward (deltas) passes
-    through the model (for a mini-batch), which is required to compute
-    the gradients for the parameters
-    """
-    def __init__(self, cost, rng=None):
-
-        assert isinstance(cost, Cost), (
-            "Cost needs to be of type mlp.costs.Cost, got %s" % type(cost)
-        )
-
-        self.layers = [] #the actual list of network layers
-        self.activations = [] #keeps forward-pass activations (h from equations)
-                              # for a given minibatch (or features at 0th index)
-        self.deltas = [] #keeps back-propagated error signals (deltas from equations)
-                         # for a given minibatch and each layer
-        self.cost = cost
-
-        if rng is None:
-            self.rng = numpy.random.RandomState([2015,11,11])
-        else:
-            self.rng = rng
-
-    def fprop(self, x):
-        """
-
-        :param inputs: mini-batch of data-points x
-        :return: y (top layer activation) which is an estimate of y given x
-        """
-
-        if len(self.activations) != len(self.layers) + 1:
-            self.activations = [None]*(len(self.layers) + 1)
-
-        self.activations[0] = x
-        for i in xrange(0, len(self.layers)):
-            self.activations[i+1] = self.layers[i].fprop(self.activations[i])
-        return self.activations[-1]
-
-    def fprop_dropout(self, x, dp_scheduler):
-        """
-        :param inputs: mini-batch of data-points x
-        :param dp_scheduler: dropout scheduler
-        :return: y (top layer activation) which is an estimate of y given x
-        """
-
-        if len(self.activations) != len(self.layers) + 1:
-            self.activations = [None]*(len(self.layers) + 1)
-
-        p_inp, p_hid = dp_scheduler.get_rate()
-
-        d_inp = 1
-        p_inp_scaler, p_hid_scaler = 1.0/p_inp, 1.0/p_hid
-        if p_inp < 1:
-            d_inp = self.rng.binomial(1, p_inp, size=x.shape)
-
-        self.activations[0] = p_inp_scaler*d_inp*x #it's OK to scale the inputs by p_inp_scaler here
-        self.activations[1] = self.layers[0].fprop(self.activations[0])
-        for i in xrange(1, len(self.layers)):
-            d_hid = 1
-            if p_hid < 1:
-                d_hid = self.rng.binomial(1, p_hid, size=self.activations[i].shape)
-            self.activations[i] *= d_hid #but not the hidden activations, since the non-linearity grad *may* explicitly depend on them
-            self.activations[i+1] = self.layers[i].fprop(p_hid_scaler*self.activations[i])
-
-        return self.activations[-1]
-
-    def bprop(self, cost_grad, dp_scheduler=None):
-        """
-        :param cost_grad: matrix -- grad of the cost w.r.t y
-        :return: None, the deltas are kept in the model
-        """
-
-        # allocate the list of deltas for each layer
-        # note, we do not use all of those fields but
-        # want to keep it aligned 1:1 with activations,
-        # which will simplify indexing later on when
-        # computing grads w.r.t parameters
-        if len(self.deltas) != len(self.activations):
-            self.deltas = [None]*len(self.activations)
-
-        # treat the top layer in special way, as it deals with the
-        # cost, which may lead to some simplifications
-        top_layer_idx = len(self.layers)
-        self.deltas[top_layer_idx], ograds = self.layers[top_layer_idx - 1].\
-            bprop_cost(self.activations[top_layer_idx], cost_grad, self.cost)
-
-        p_hid_scaler = 1.0
-        if dp_scheduler is not None:
-            p_inp, p_hid = dp_scheduler.get_rate()
-            p_hid_scaler /= p_hid
-
-        # then back-prop through remaining layers
-        for i in xrange(top_layer_idx - 1, 0, -1):
-            self.deltas[i], ograds = self.layers[i - 1].\
-                bprop(self.activations[i], ograds*p_hid_scaler)
-
-    def add_layer(self, layer):
-        self.layers.append(layer)
-
-    def set_layers(self, layers):
-        self.layers = layers
-
-    def get_name(self):
-        return 'mlp'
 
 
 class Layer(object):
+    """Abstract class defining the interface for a layer."""
+
+    def fprop(self, inputs):
+        """Forward propagates activations through the layer transformation.
+
+        Args:
+            inputs: Array of layer inputs of shape (batch_size, input_dim).
+
+        Returns:
+            outputs: Array of layer outputs of shape (batch_size, output_dim).
+        """
+        raise NotImplementedError()
+
+    def bprop(self, inputs, outputs, grads_wrt_outputs):
+        """Back propagates gradients through a layer.
+
+        Given gradients with respect to the outputs of the layer calculates the
+        gradients with respect to the layer inputs.
+
+        Args:
+            inputs: Array of layer inputs of shape (batch_size, input_dim).
+            outputs: Array of layer outputs calculated in forward pass of
+                shape (batch_size, output_dim).
+            grads_wrt_outputs: Array of gradients with respect to the layer
+                outputs of shape (batch_size, output_dim).
+
+        Returns:
+            Array of gradients with respect to the layer inputs of shape
+            (batch_size, input_dim).
+        """
+        raise NotImplementedError()
+
+
+class LayerWithParameters(Layer):
+    """Abstract class defining the interface for a layer with parameters."""
+
+    def grads_wrt_params(self, inputs, grads_wrt_outputs):
+        """Calculates gradients with respect to layer parameters.
+
+        Args:
+            inputs: Array of inputs to layer of shape (batch_size, input_dim).
+            grads_wrt_to_outputs: Array of gradients with respect to the layer
+                outputs of shape (batch_size, output_dim).
+
+        Returns:
+            List of arrays of gradients with respect to the layer parameters
+            with parameter gradients appearing in same order in tuple as
+            returned from `get_params` method.
+        """
+        raise NotImplementedError()
+
+    def params_cost(self):
+        """Returns the parameter dependent cost term for this layer.
+
+        If no parameter-dependent cost terms are set this returns zero.
+        """
+        raise NotImplementedError()
+
+    @property
+    def params(self):
+        """Returns a list of parameters of layer.
+
+        Returns:
+            List of current parameter values. This list should be in the
+            corresponding order to the `values` argument to `set_params`.
+        """
+        raise NotImplementedError()
+
+    @params.setter
+    def params(self, values):
+        """Sets layer parameters from a list of values.
+
+        Args:
+            values: List of values to set parameters to. This list should be
+                in the corresponding order to what is returned by `get_params`.
+        """
+        raise NotImplementedError()
+
+
+class AffineLayer(LayerWithParameters):
+    """Layer implementing an affine tranformation of its inputs.
+
+    This layer is parameterised by a weight matrix and bias vector.
     """
-    Abstract class defining an interface for
-    other transforms.
-    """
-    def __init__(self, rng=None):
 
-        if rng is None:
+    def __init__(self, input_dim, output_dim,
-            seed=[2015, 10, 1]
+                 weights_initialiser=init.UniformInit(-0.1, 0.1),
-            self.rng = numpy.random.RandomState(seed)
+                 biases_initialiser=init.ConstantInit(0.),
-        else:
+                 weights_cost=None, biases_cost=None):
-            self.rng = rng
+        """Initialises a parameterised affine layer.
+
+        Args:
+            input_dim (int): Dimension of inputs to the layer.
+            output_dim (int): Dimension of the layer outputs.
+            weights_initialiser: Initialiser for the weight parameters.
+            biases_initialiser: Initialiser for the bias parameters.
+            weights_cost: Weights-dependent cost term.
+            biases_cost: Biases-dependent cost term.
+        """
+        self.input_dim = input_dim
+        self.output_dim = output_dim
+        self.weights = weights_initialiser((self.output_dim, self.input_dim))
+        self.biases = biases_initialiser(self.output_dim)
+        self.weights_cost = weights_cost
+        self.biases_cost = biases_cost
 
     def fprop(self, inputs):
-        """
+        """Forward propagates activations through the layer transformation.
-        Implements a forward propagation through the i-th layer, that is
-        some form of:
-           a^i = xW^i + b^i
-           h^i = f^i(a^i)
-        with f^i, W^i, b^i denoting a non-linearity, weight matrix and
-        biases at the i-th layer, respectively and x denoting inputs.
 
-        :param inputs: matrix of features (x) or the output of the previous layer h^{i-1}
+        For inputs `x`, outputs `y`, weights `W` and biases `b` the layer
-        :return: h^i, matrix of transformed by layer features
+        corresponds to `y = W.dot(x) + b`.
-        """
-        raise NotImplementedError()
-    
-    def bprop(self, h, igrads):
-        """
-        Implements a backward propagation through the layer, that is, given
-        h^i denotes the output of the layer and x^i the input, we compute:
-        dh^i/dx^i which by chain rule is dh^i/da^i da^i/dx^i
-        x^i could be either features (x) or the output of the lower layer h^{i-1}
-        :param h: it's an activation produced in forward pass
-        :param igrads, error signal (or gradient) flowing to the layer, note,
-               this in general case does not corresponds to 'deltas' used to update
-               the layer's parameters, to get deltas ones need to multiply it with
-               the dh^i/da^i derivative
-        :return: a tuple (deltas, ograds) where:
-               deltas = igrads * dh^i/da^i
-               ograds = deltas \times da^i/dx^i
-        """
-        raise NotImplementedError()
 
-    def bprop_cost(self, h, igrads, cost=None):
+        Args:
+            inputs: Array of layer inputs of shape (batch_size, input_dim).
+
+        Returns:
+            outputs: Array of layer outputs of shape (batch_size, output_dim).
         """
-        Implements a backward propagation in case the layer directly
+        return self.weights.dot(inputs.T).T + self.biases
-        deals with the optimised cost (i.e. the top layer)
+
-        By default, method should implement a back-prop for default cost, that is
+    def bprop(self, inputs, outputs, grads_wrt_outputs):
-        the one that is natural to the layer's output, i.e.:
+        """Back propagates gradients through a layer.
-        linear -> mse, softmax -> cross-entropy, sigmoid -> binary cross-entropy
+
-        :param h: it's an activation produced in forward pass
+        Given gradients with respect to the outputs of the layer calculates the
-        :param igrads, error signal (or gradient) flowing to the layer, note,
+        gradients with respect to the layer inputs.
-               this in general case does not corresponds to 'deltas' used to update
+
-               the layer's parameters, to get deltas ones need to multiply it with
+        Args:
-               the dh^i/da^i derivative
+            inputs: Array of layer inputs of shape (batch_size, input_dim).
-        :return: a tuple (deltas, ograds) where:
+            outputs: Array of layer outputs calculated in forward pass of
-               deltas = igrads * dh^i/da^i
+                shape (batch_size, output_dim).
-               ograds = deltas \times da^i/dx^i
+            grads_wrt_outputs: Array of gradients with respect to the layer
+                outputs of shape (batch_size, output_dim).
+
+        Returns:
+            Array of gradients with respect to the layer inputs of shape
+            (batch_size, input_dim).
+        """
+        return grads_wrt_outputs.dot(self.weights)
+
+    def grads_wrt_params(self, inputs, grads_wrt_outputs):
+        """Calculates gradients with respect to layer parameters.
+
+        Args:
+            inputs: array of inputs to layer of shape (batch_size, input_dim)
+            grads_wrt_to_outputs: array of gradients with respect to the layer
+                outputs of shape (batch_size, output_dim)
+
+        Returns:
+            list of arrays of gradients with respect to the layer parameters
+            `[grads_wrt_weights, grads_wrt_biases]`.
         """
 
-        raise NotImplementedError()
+        grads_wrt_weights = np.dot(grads_wrt_outputs.T, inputs)
+        grads_wrt_biases = np.sum(grads_wrt_outputs, axis=0)
 
-    def pgrads(self, inputs, deltas, **kwargs):
+        if self.weights_cost is not None:
+            grads_wrt_weights += self.weights_cost.grad(self.weights)
+
+        if self.biases_cost is not None:
+            grads_wrt_biases += self.biases_cost.grads(self.biases)
+
+        return [grads_wrt_weights, grads_wrt_biases]
+
+    def params_cost(self):
+        """Returns the parameter dependent cost term for this layer.
+
+        If no parameter-dependent cost terms are set this returns zero.
         """
-        Return gradients w.r.t parameters
+        params_cost = 0
-        """
+        if self.weights_cost is not None:
-        raise NotImplementedError()
+            params_cost += self.weights_cost(self.weights)
+        if self.biases_cost is not None:
+            params_cost += self.biases_cost(self.biases)
+        return params_cost
 
-    def get_params(self):
+    @property
-        raise NotImplementedError()
+    def params(self):
+        """A list of layer parameter values: `[weights, biases]`."""
+        return [self.weights, self.biases]
 
-    def set_params(self):
+    @params.setter
-        raise NotImplementedError()
+    def params(self, values):
+        self.weights = values[0]
+        self.biases = values[1]
 
-    def get_name(self):
+    def __repr__(self):
-        return 'abstract_layer'
+        return 'AffineLayer(input_dim={0}, output_dim={1})'.format(
+            self.input_dim, self.output_dim)
 
 
-class Linear(Layer):
+class SigmoidLayer(Layer):
-
+    """Layer implementing an element-wise logistic sigmoid transformation."""
-    def __init__(self, idim, odim,
-                 rng=None,
-                 irange=0.1):
-
-        super(Linear, self).__init__(rng=rng)
-
-        self.idim = idim
-        self.odim = odim
-
-        self.W = self.rng.uniform(
-            -irange, irange,
-            (self.idim, self.odim))
-
-        self.b = numpy.zeros((self.odim,), dtype=numpy.float32)
 
     def fprop(self, inputs):
+        """Forward propagates activations through the layer transformation.
+
+        For inputs `x` and outputs `y` this corresponds to
+        `y = 1 / (1 + exp(-x))`.
+
+        Args:
+            inputs: Array of layer inputs of shape (batch_size, input_dim).
+
+        Returns:
+            outputs: Array of layer outputs of shape (batch_size, output_dim).
         """
-        Implements a forward propagation through the i-th layer, that is
+        return 1. / (1. + np.exp(-inputs))
-        some form of:
-           a^i = xW^i + b^i
-           h^i = f^i(a^i)
-        with f^i, W^i, b^i denoting a non-linearity, weight matrix and
-        biases of this (i-th) layer, respectively and x denoting inputs.
 
-        :param inputs: matrix of features (x) or the output of the previous layer h^{i-1}
+    def bprop(self, inputs, outputs, grads_wrt_outputs):
-        :return: h^i, matrix of transformed by layer features
+        """Back propagates gradients through a layer.
+
+        Given gradients with respect to the outputs of the layer calculates the
+        gradients with respect to the layer inputs.
+
+        Args:
+            inputs: Array of layer inputs of shape (batch_size, input_dim).
+            outputs: Array of layer outputs calculated in forward pass of
+                shape (batch_size, output_dim).
+            grads_wrt_outputs: Array of gradients with respect to the layer
+                outputs of shape (batch_size, output_dim).
+
+        Returns:
+            Array of gradients with respect to the layer inputs of shape
+            (batch_size, input_dim).
         """
+        return grads_wrt_outputs * outputs * (1. - outputs)
 
-        #input comes from 4D convolutional tensor, reshape to expected shape
+    def __repr__(self):
-        if inputs.ndim == 4:
+        return 'SigmoidLayer'
-            inputs = inputs.reshape(inputs.shape[0], -1)
-
-        a = numpy.dot(inputs, self.W) + self.b
-        # here f() is an identity function, so just return a linear transformation
-        return a
-
-    def bprop(self, h, igrads):
-        """
-        Implements a backward propagation through the layer, that is, given
-        h^i denotes the output of the layer and x^i the input, we compute:
-        dh^i/dx^i which by chain rule is dh^i/da^i da^i/dx^i
-        x^i could be either features (x) or the output of the lower layer h^{i-1}
-        :param h: it's an activation produced in forward pass
-        :param igrads, error signal (or gradient) flowing to the layer, note,
-               this in general case does not corresponds to 'deltas' used to update
-               the layer's parameters, to get deltas ones need to multiply it with
-               the dh^i/da^i derivative
-        :return: a tuple (deltas, ograds) where:
-               deltas = igrads * dh^i/da^i
-               ograds = deltas \times da^i/dx^i
-        """
-
-        # since df^i/da^i = 1 (f is assumed identity function),
-        # deltas are in fact the same as igrads
-        ograds = numpy.dot(igrads, self.W.T)
-        return igrads, ograds
-
-    def bprop_cost(self, h, igrads, cost):
-        """
-        Implements a backward propagation in case the layer directly
-        deals with the optimised cost (i.e. the top layer)
-        By default, method should implement a bprop for default cost, that is
-        the one that is natural to the layer's output, i.e.:
-        here we implement linear -> mse scenario
-        :param h: it's an activation produced in forward pass
-        :param igrads, error signal (or gradient) flowing to the layer, note,
-               this in general case does not corresponds to 'deltas' used to update
-               the layer's parameters, to get deltas ones need to multiply it with
-               the dh^i/da^i derivative
-        :param cost, mlp.costs.Cost instance defining the used cost
-        :return: a tuple (deltas, ograds) where:
-               deltas = igrads * dh^i/da^i
-               ograds = deltas \times da^i/dx^i
-        """
-
-        if cost is None or cost.get_name() == 'mse':
-            # for linear layer and mean square error cost,
-            # cost back-prop is the same as standard back-prop
-            return self.bprop(h, igrads)
-        else:
-            raise NotImplementedError('Linear.bprop_cost method not implemented '
-                                      'for the %s cost' % cost.get_name())
-
-    def pgrads(self, inputs, deltas, l1_weight=0, l2_weight=0):
-        """
-        Return gradients w.r.t parameters
-
-        :param inputs, input to the i-th layer
-        :param deltas, deltas computed in bprop stage up to -ith layer
-        :param kwargs, key-value optional arguments
-        :return list of grads w.r.t parameters dE/dW and dE/db in *exactly*
-                the same order as the params are returned by get_params()
-
-        Note: deltas here contain the whole chain rule leading
-        from the cost up to the the i-th layer, i.e.
-        dE/dy^L dy^L/da^L da^L/dh^{L-1} dh^{L-1}/da^{L-1} ... dh^{i}/da^{i}
-        and here we are just asking about
-          1) da^i/dW^i and 2) da^i/db^i
-        since W and b are only layer's parameters
-        """
-
-        #input comes from 4D convolutional tensor, reshape to expected shape
-        if inputs.ndim == 4:
-            inputs = inputs.reshape(inputs.shape[0], -1)
-
-        #you could basically use different scalers for biases
-        #and weights, but it is not implemented here like this
-        l2_W_penalty, l2_b_penalty = 0, 0
-        if l2_weight > 0:
-            l2_W_penalty = l2_weight*self.W
-            l2_b_penalty = l2_weight*self.b
-
-        l1_W_penalty, l1_b_penalty = 0, 0
-        if l1_weight > 0:
-            l1_W_penalty = l1_weight*numpy.sign(self.W)
-            l1_b_penalty = l1_weight*numpy.sign(self.b)
-
-        grad_W = numpy.dot(inputs.T, deltas) + l2_W_penalty + l1_W_penalty
-        grad_b = numpy.sum(deltas, axis=0) + l2_b_penalty + l1_b_penalty
-
-        return [grad_W, grad_b]
-
-    def get_params(self):
-        return [self.W, self.b]
-
-    def set_params(self, params):
-        #we do not make checks here, but the order on the list
-        #is assumed to be exactly the same as get_params() returns
-        self.W = params[0]
-        self.b = params[1]
-
-    def get_name(self):
-        return 'linear'
 
 
-class Sigmoid(Linear):
+class ReluLayer(Layer):
-    def __init__(self,  idim, odim,
+    """Layer implementing an element-wise rectified linear transformation."""
-                 rng=None,
-                 irange=0.1):
-
-        super(Sigmoid, self).__init__(idim, odim, rng, irange)
-    
-    def fprop(self, inputs):
-        #get the linear activations
-        a = super(Sigmoid, self).fprop(inputs)
-        #stabilise the exp() computation in case some values in
-        #'a' get very negative. We limit both tails, however only
-        #negative values may lead to numerical issues -- exp(-a)
-        #clip() function does the following operation faster:
-        # a[a < -30.] = -30,
-        # a[a > 30.] = 30.
-        numpy.clip(a, -30.0, 30.0, out=a)
-        h = 1.0/(1 + numpy.exp(-a))
-        return h
-    
-    def bprop(self, h, igrads):
-        dsigm = h * (1.0 - h)
-        deltas = igrads * dsigm
-        ___, ograds = super(Sigmoid, self).bprop(h=None, igrads=deltas)
-        return deltas, ograds
-
-    def bprop_cost(self, h, igrads, cost):
-        if cost is None or cost.get_name() == 'bce':
-            return super(Sigmoid, self).bprop(h=h, igrads=igrads)
-        else:
-            raise NotImplementedError('Sigmoid.bprop_cost method not implemented '
-                                      'for the %s cost' % cost.get_name())
-
-    def get_name(self):
-        return 'sigmoid'
-
-
-class Softmax(Linear):
-
-    def __init__(self,idim, odim,
-                 rng=None,
-                 irange=0.1):
-
-        super(Softmax, self).__init__(idim,
-                                      odim,
-                                      rng=rng,
-                                      irange=irange)
 
     def fprop(self, inputs):
+        """Forward propagates activations through the layer transformation.
 
-        # compute the linear outputs
+        For inputs `x` and outputs `y` this corresponds to `y = max(0, x)`.
-        a = super(Softmax, self).fprop(inputs)
-        # apply numerical stabilisation by subtracting max
-        # from each row (not required for the coursework)
-        # then compute exponent
-        assert a.ndim in [1, 2], (
-            "Expected the linear activation in Softmax layer to be either "
-            "vector or matrix, got %ith dimensional tensor" % a.ndim
-        )
-        axis = a.ndim - 1
-        exp_a = numpy.exp(a - numpy.max(a, axis=axis, keepdims=True))
-        # finally, normalise by the sum within each example
-        y = exp_a/numpy.sum(exp_a, axis=axis, keepdims=True)
 
-        return y
+        Args:
+            inputs: Array of layer inputs of shape (batch_size, input_dim).
 
-    def bprop(self, h, igrads):
+        Returns:
-        raise NotImplementedError('Softmax.bprop not implemented for hidden layer.')
+            outputs: Array of layer outputs of shape (batch_size, output_dim).
+        """
+        return np.maximum(inputs, 0.)
 
-    def bprop_cost(self, h, igrads, cost):
+    def bprop(self, inputs, outputs, grads_wrt_outputs):
+        """Back propagates gradients through a layer.
 
-        if cost is None or cost.get_name() == 'ce':
+        Given gradients with respect to the outputs of the layer calculates the
-            return super(Softmax, self).bprop(h=h, igrads=igrads)
+        gradients with respect to the layer inputs.
-        else:
-            raise NotImplementedError('Softmax.bprop_cost method not implemented '
-                                      'for %s cost' % cost.get_name())
 
-    def get_name(self):
+        Args:
-        return 'softmax'
+            inputs: Array of layer inputs of shape (batch_size, input_dim).
+            outputs: Array of layer outputs calculated in forward pass of
+                shape (batch_size, output_dim).
+            grads_wrt_outputs: Array of gradients with respect to the layer
+                outputs of shape (batch_size, output_dim).
+
+        Returns:
+            Array of gradients with respect to the layer inputs of shape
+            (batch_size, input_dim).
+        """
+        return (outputs > 0) * grads_wrt_outputs
+
+    def __repr__(self):
+        return 'ReluLayer'
 
 
-class Relu(Linear):
+class TanhLayer(Layer):
-    def __init__(self,  idim, odim,
+    """Layer implementing an element-wise hyperbolic tangent transformation."""
-                 rng=None,
-                 irange=0.1):
-
-        super(Relu, self).__init__(idim, odim, rng, irange)
 
     def fprop(self, inputs):
-        #get the linear activations
+        """Forward propagates activations through the layer transformation.
-        a = super(Relu, self).fprop(inputs)
-        h = numpy.clip(a, 0, 20.0)
-        #h = numpy.maximum(a, 0)
-        return h
 
-    def bprop(self, h, igrads):
+        For inputs `x` and outputs `y` this corresponds to `y = tanh(x)`.
-        deltas = (h > 0)*igrads
-        ___, ograds = super(Relu, self).bprop(h=None, igrads=deltas)
-        return deltas, ograds
 
-    def bprop_cost(self, h, igrads, cost):
+        Args:
-        raise NotImplementedError('Relu.bprop_cost method not implemented '
+            inputs: Array of layer inputs of shape (batch_size, input_dim).
-                                      'for the %s cost' % cost.get_name())
 
-    def get_name(self):
+        Returns:
-        return 'relu'
+            outputs: Array of layer outputs of shape (batch_size, output_dim).
+        """
+        return np.tanh(inputs)
 
+    def bprop(self, inputs, outputs, grads_wrt_outputs):
+        """Back propagates gradients through a layer.
 
-class Tanh(Linear):
+        Given gradients with respect to the outputs of the layer calculates the
-    def __init__(self,  idim, odim,
+        gradients with respect to the layer inputs.
-                 rng=None,
-                 irange=0.1):
 
-        super(Tanh, self).__init__(idim, odim, rng, irange)
+        Args:
+            inputs: Array of layer inputs of shape (batch_size, input_dim).
+            outputs: Array of layer outputs calculated in forward pass of
+                shape (batch_size, output_dim).
+            grads_wrt_outputs: Array of gradients with respect to the layer
+                outputs of shape (batch_size, output_dim).
 
-    def fprop(self, inputs):
+        Returns:
-        #get the linear activations
+            Array of gradients with respect to the layer inputs of shape
-        a = super(Tanh, self).fprop(inputs)
+            (batch_size, input_dim).
-        numpy.clip(a, -30.0, 30.0, out=a)
+        """
-        h = numpy.tanh(a)
+        return (1. - outputs**2) * grads_wrt_outputs
-        return h
 
-    def bprop(self, h, igrads):
+    def __repr__(self):
-        deltas = (1.0 - h**2) * igrads
+        return 'TanhLayer'
-        ___, ograds = super(Tanh, self).bprop(h=None, igrads=deltas)
-        return deltas, ograds
-
-    def bprop_cost(self, h, igrads, cost):
-        raise NotImplementedError('Tanh.bprop_cost method not implemented '
-                                      'for the %s cost' % cost.get_name())
-
-    def get_name(self):
-        return 'tanh'
-
-
-class Maxout(Linear):
-    def __init__(self,  idim, odim, k,
-                 rng=None,
-                 irange=0.05):
-
-        super(Maxout, self).__init__(idim, odim*k, rng, irange)
-
-        self.max_odim = odim
-        self.k = k
-
-    def fprop(self, inputs):
-        #get the linear activations
-        a = super(Maxout, self).fprop(inputs)
-        ar = a.reshape(a.shape[0], self.max_odim, self.k)
-        h, h_argmax = max_and_argmax(ar, axes=2, keepdims_max=True, keepdims_argmax=True)
-        self.h_argmax = h_argmax
-        return h[:, :, 0] #get rid of the last reduced dimensison (of size 1)
-
-    def bprop(self, h, igrads):
-        #hack for dropout backprop (ignore dropped neurons). Note, this is not
-        #entirely correct when h fires at 0 exaclty (but is not dropped, in which case
-        #derivative should be 1). However, this is rather unlikely to happen (that h fires as 0)
-        #and probably can be ignored for now. Otherwise, one would have to keep the dropped unit
-        #indexes and zero grads according to them.
-        igrads = (h != 0)*igrads
-        #convert into the shape where upsampling is easier
-        igrads_up = igrads.reshape(igrads.shape[0], self.max_odim, 1)
-        #upsample to the linear dimension (but reshaped to (batch_size, maxed_num (1), pool_size)
-        igrads_up = numpy.tile(igrads_up, (1, 1, self.k))
-        #generate mask matrix and set to 1 maxed elements
-        mask = numpy.zeros_like(igrads_up)
-        mask[self.h_argmax] = 1.0
-        #do bprop through max operator and then reshape into 2D
-        deltas = (igrads_up * mask).reshape(igrads_up.shape[0], -1)
-        #and then do bprop thorough linear part
-        ___, ograds = super(Maxout, self).bprop(h=None, igrads=deltas)
-        return deltas, ograds
-
-    def bprop_cost(self, h, igrads, cost):
-        raise NotImplementedError('Maxout.bprop_cost method not implemented '
-                                      'for the %s cost' % cost.get_name())
-
-    def get_name(self):
-        return 'maxout'

mlp/learning_rules.py

@@ -0,0 +1,42 @@
+"""Learning rules."""
+
+import numpy as np
+
+
+class GradientDescentLearningRule(object):
+
+    def __init__(self, learning_rate=1e-3):
+        self.learning_rate = learning_rate
+
+    def initialise(self, params):
+        self.params = params
+
+    def reset(self):
+        pass
+
+    def update_params(self, grads_wrt_params):
+        for param, grad in zip(self.params, grads_wrt_params):
+            param -= self.learning_rate * grad
+
+
+class MomentumLearningRule(object):
+
+    def __init__(self, learning_rate=1e-3, mom_coeff=0.9):
+        self.learning_rate = learning_rate
+        self.mom_coeff = mom_coeff
+
+    def initialise(self, params):
+        self.params = params
+        self.moms = []
+        for param in self.params:
+            self.moms.append(np.zeros_like(param))
+
+    def reset(self):
+        for mom in zip(self.moms):
+            mom *= 0.
+
+    def update_params(self, grads_wrt_params):
+        for param, mom, grad in zip(self.params, self.moms, grads_wrt_params):
+            mom *= self.mom_coeff
+            mom -= self.learning_rate * grad
+            param += mom

mlp/models.py

@@ -0,0 +1,92 @@
+"""
+Model definitions.
+"""
+
+from mlp.layers import LayerWithParameters
+
+
+class SingleLayerModel(object):
+    """
+    """
+    def __init__(self, layer):
+        self.layer = layer
+
+    @property
+    def params(self):
+        """
+        """
+        return self.layer.params
+
+    def fprop(self, inputs):
+        """
+        """
+        activations = [inputs, self.layer.fprop(inputs)]
+        return activations
+
+    def grads_wrt_params(self, activations, grads_wrt_outputs):
+        """
+        """
+        return self.layer.grads_wrt_params(activations[0], grads_wrt_outputs)
+
+    def params_cost(self):
+        """
+        """
+        return self.layer.params_cost()
+
+    def __repr__(self):
+        return 'SingleLayerModel(' + str(layer) + ')'
+
+
+class MultipleLayerModel(object):
+    """
+    """
+    def __init__(self, layers):
+        self.layers = layers
+
+    @property
+    def params(self):
+        """
+        """
+        params = []
+        for layer in self.layers:
+            if isinstance(layer, LayerWithParameters):
+                params += layer.params
+        return params
+
+    def fprop(self, inputs):
+        """
+        """
+        activations = [inputs]
+        for i, layer in enumerate(self.layers):
+            activations.append(self.layers[i].fprop(activations[i]))
+        return activations
+
+    def grads_wrt_params(self, activations, grads_wrt_outputs):
+        """
+        """
+        grads_wrt_params = []
+        for i, layer in enumerate(self.layers[::-1]):
+            inputs = activations[-i - 2]
+            outputs = activations[-i - 1]
+            grads_wrt_inputs = layer.bprop(inputs, outputs, grads_wrt_outputs)
+            if isinstance(layer, LayerWithParameters):
+                grads_wrt_params += layer.grads_wrt_params(
+                    inputs, grads_wrt_outputs)[::-1]
+            grads_wrt_outputs = grads_wrt_inputs
+        return grads_wrt_params[::-1]
+
+    def params_cost(self):
+        """
+        """
+        params_cost = 0.
+        for layer in self.layers:
+            if isinstance(layer, LayerWithParameters):
+                params_cost += layer.params_cost()
+        return params_cost
+
+    def __repr__(self):
+        return (
+            'MultiLayerModel(\n    ' +
+            '\n    '.join([str(layer) for layer in self.layers]) +
+            '\n)'
+        )

mlp/trainers.py

@@ -0,0 +1,65 @@
+"""Model trainers."""
+
+import time
+import logging
+from collections import OrderedDict
+
+
+logger = logging.getLogger(__name__)
+
+
+class Trainer(object):
+
+    def __init__(self, model, cost, learning_rule, train_dataset,
+                 valid_dataset=None):
+        self.model = model
+        self.cost = cost
+        self.learning_rule = learning_rule
+        self.learning_rule.initialise(self.model.params)
+        self.train_dataset = train_dataset
+        self.valid_dataset = valid_dataset
+
+    def do_training_epoch(self):
+        for inputs_batch, targets_batch in self.train_dataset:
+            activations = self.model.fprop(inputs_batch)
+            grads_wrt_outputs = self.cost.grad(activations[-1], targets_batch)
+            grads_wrt_params = self.model.grads_wrt_params(
+                activations, grads_wrt_outputs)
+            self.learning_rule.update_params(grads_wrt_params)
+        self.train_dataset.reset()
+
+    def data_cost(self, dataset):
+        cost = 0.
+        for inputs_batch, targets_batch in dataset:
+            activations = self.model.fprop(inputs_batch)
+            cost += self.cost(activations[-1], targets_batch)
+        dataset.reset()
+        return cost
+
+    def get_epoch_stats(self):
+        epoch_stats = OrderedDict()
+        epoch_stats['cost(train)'] = self.data_cost(
+            self.train_dataset)
+        epoch_stats['cost(valid)'] = self.data_cost(
+            self.valid_dataset)
+        epoch_stats['cost(param)'] = self.model.params_cost()
+        return epoch_stats
+
+    def log_stats(self, epoch, stats):
+        logger.info('Epoch {0}: {1}'.format(
+            epoch,
+            ', '.join(['{0}={1:.3f}'.format(k, v) for (k, v) in stats.items()])
+        ))
+
+    def train(self, n_epochs, stats_interval=5):
+        run_stats = []
+        for epoch in range(n_epochs):
+            start_time = time.clock()
+            self.do_training_epoch()
+            epoch_time = time.clock() - start_time
+            if epoch % stats_interval == 0:
+                stats = self.get_epoch_stats()
+                stats['time'] = epoch_time
+                self.log_stats(epoch, stats)
+                run_stats.append(stats.items())
+        return np.array(run_stats), stats.keys()